The present invention relates to an interface for connecting a data-processing unit to an automatic diagnosis system, and more particularly to means for controlling and implementing such an interface.
The circuits of data-processing units are normally complex. In the event of faults in such units, a diagnosis performed by manual or semi-automatic means is lengthy and laborious, and, therefore, reliance has increasingly been placed on automatic methods of testing and diagnosis. In the main, these automatic methods consist of carrying out in a computer special programs for diagnosing the unit to be investigated. When these programs are carried out, test data is fed into the unit concerned via an interface which connects it to the diagnosis computer system, and the data resulting from the test is transmitted by the unit to this system, generally via the same interface. Among the data which is transmitted by the unit being tested to the diagnosis system, those items which represent fault symptoms are identified from the addresses (contained in the program being carried out) of the parts of the unit into which the test data was written in the first place. The interface via which the unit to be diagnosed is connected to the diagnosis system contains signal transmission lines which are combined into channels. The signals transmitted along these lines represent on the one hand the information exchanged between the system and the unit to be diagnosed and on the other hand the commands by which these exchanges are made.
Since a unit being diagnosed does not generally operate synchronously with the diagnosis system connected to it, adapting means are required to set up dialogues between the unit and the system along the said transmission lines. In known diagnosis systems, the adapters are so designed that the dialogues are carried on by means of a maintenance panel or console through which signals giving the status of the unit being tested pass before they are transmitted via the adapter and lines to the external diagnosis system. In particular, such adapting means allow a unit to be tested and diagnosed only when it is not operating, and it is possible that the location of a fault in the unit may be delayed or even falsified by the further sources of error which result from inserting circuits between the unit proper and the diagnosis system.
Interfaces have also been developed to allow data to be exchanged between the diagnosis system and the unit to be diagnosed by means of a limited number of connecting channels. Such interfaces include means for generating signals for controlling the exchange of data on the lines. These means are divided among the input/output circuits of the system and the unit. Such additional circuits contained in the unit may become an additional source of error which delays the process of finding the fault in the unit concerned.
One of the objects of the present invention is to enable a data-processing unit to be diagnosed quickly when operating.
Another object of the invention is to provide reliable diagnosis of a data-processing unit by means of a minimum of test circuits.
In accordance with a principal feature of the invention, the interface for connecting a data-processing unit to an automatic diagnosis system includes a set of signal transmission lines which are connected to the unit and to the system so as to allow the system to diagnose the unit. The diagnosis is achieved by a succession of operations involving writing data into, and reading data out of, the unit and by processing this data character-by-character. In accordance with the invention, such an interface includes a set of lines comprising:
a first group of lines for the bidirectional transmission, character-by-character, of the data to be written into, or read out of, the unit by the system, the first group comprising lines equal in number to the bits which form one data character; PA0 a second group of lines for successive unidirectional transmission from the system of the addresses at which the data transmitted by the first group of lines is read by the system into or out of the unit, the second group comprising lines equal in number to the bits forming one address character; PA0 a third group of lines for controlling the exchanges of information carried out along the first and second groups of lines, the third group comprising:
a. a bidirectional parity line for transmitting parity signals associated with the address and data characters transmitted by the first and second groups of lines, PA1 b. a sub-group of unidirectional lines for transmitting, from the system, signals for controlling the exchanges of information carried out along the parity line and the first and second groups of lines, and PA1 c. a unidirectional event line for transmitting signals from the unit to report asynchronous events occurring in the unit.